The drain has to be "free-flow" into the oil pan above the oil level in the pan.

If you don't have a free return the oil will back up into the bearing housing. You will have a "hydraulic" condition preventing fresh oil from the inlet supply line. The turbocharger will be lacking oil for lubrication and cooling. You will burn up your bearings and turbine shaft.

The most common turbo failure is from FOD damage, the next comes from a worn engine. High crankcase pressure from worn rings will give us the oil restriction mentioned above.

Zero hit it on the nose..on our drag engines with twin turbo I tried to locate to low and was not good..Common sense failed due to a brain fart...keep return line as large and straight as possible with no chance to kink...60 series in prevo yet? Mine on stand in shop with Eaton attached-all preped and ready to install.. Bob

Thanks for the replies. It was not what I wanted to hear but it's what I thought was the correct answer. If I could switch sides for the drain back on this Series 50 engine swap I'm doing the installation would be a little cleaner. So far I don't see any place on the intake side of the block with a fitting or plate that can I use for drain back. The oil fill tube is on that side and it's about 1 1/2" diameter. Do you think if I tee into it a few inches above the oil level that would work? Robert I have not touched my bus. I still have a few weeks left on this Silversides repower.